1. Field of the Invention
This invention is directed to method and apparatus for accumulator systems for maintaining proper line tension during the winding of filamentary material such as wire or cable from a primary source of filamentary material such as the apparatus for making the filamentary material or a secondary source such as a spool of filamentary material, and more particularly to such apparatus and method using a plurality of serially connected active accumulator elements which are interdependently controlled from a programmed controller.
2. Related Art
U.S. Pat. No. 3,282,488 issued to Bauer et al. Nov. 1, 1966, discloses a web conveying apparatus using an overrunning clutch assembly geared to a dancer roll to power the vertical descent of the dancer roll and limit its descent speed in a system employing a plurality of rotary transport rolls engageable with a web to be transported.
U.S. Pat. No. 3,540,641 issued to Besnyo Nov. 17, 1970, relates to a web accumulator for maintaining a substantially uniform web tension in which a pair of opposed arms are mounted for swinging movement at opposite ends of a frame. A plurality of rollers are located at spaced intervals along the arms and the web is conducted alternately over a roller at the outer end of one arm and a roller at the inner end of the other arm and progressively back and forth over the rollers of both arms and then off the frame at the opposite end. The arms swing in coordinated relation to provide wide variation of spacing and the arms are powered to swing when the tension in the web changes.
U.S. Pat. No. 3,692,251 issued to Melead Sep. 19, 1972, discloses a tensioning apparatus used with winding and unwinding apparatus for thread-like filamentary material in which a roller is mounted for rotation in members disposed at the ends of the roller and supported by pivot arms, thereby enabling horizontal movement of the roller. The moving filamentary material engages the roller to apply a horizontal force opposite to a pre-determined desired horizontal force. Changes in the tension of the filamentary material cause horizontal motion of the roller and that motion adjusts tensions by changing the speed of the filamentary material.
U.S. Pat. No. 3,871,205 issued to Fenton Mar. 18, 1975, relates to apparatus for the length stabilization of armored well logging cable wherein the cable is passed from a payoff reel over hold-back sheaves, a series of fixed sheaves, a movable sheave, and haul-off sheaves to a take-up reel. A hydraulic system controls the movable sheave to place the cable under tension. A second hydraulic system cyclically varies the effect of the hold-back sheaves to vary the cable tension.
U.S. Pat. No. 4,202,476 issued to Martin May 13, 1980, discloses web-tensioning apparatus in which fixed web-driving rollers and idler rollers are suspended from the web. A first drive sets the surface velocity of a web-driving roller and a second drive sets the surface velocities of the other web-driving rollers in response to the positions of the idler rollers to maintain substantially uniform web tension.
There are essentially five different types of large capacity accumulators presently being used for winding filamentary material, and all of them have similar drawbacks or disadvantages, namely poor regulation of tension during acceleration and deceleration of the moving filamentary material. This is caused by the large moving mass of the accumulator, unresponsive air regulators, the time the volume of air requires to flow into the hydraulic cylinders and the inertia of the pulleys or sheaves.
The horizontally opening accumulator schematically shown in FIGS. 1A, 1B and 1C is normally mounted overhead and as the filamentary material slackens it becomes a safety hazard for the operators of the accumulator.
The vertical accumulator opening down as schematically shown in FIGS. 2A, 2B and 2C has a minimum tension during static conditions, i.e. when the movable block is stationary or the output speed of the filamentary material is equal to the input speed. Minimum tension is based upon gravity applying a force on the movable block. While this may be an advantage when the accumulator is filling with filamenatary material because gravity accelerates the block downward, it is also a disadvantage when filamentary material is being pulled out faster than it is being put in. Line tension increases during this dynamic change because the filamentary material must accelerate the movable block in the opposite direction of the gravitational force. Under static conditions the minimum tension of the filamentary material equals the weight of the movable block divided by the number of wraps.
The vertical accumulator opening up schematically shown in FIGS. 3A and 3B has one advantage in that it allows the operator to easily string the accumulator with the filamentary material. However, the tensioning system must also operate against gravity and when low tensions are desired there is not enough force to open the accumulator during filling of the filamentary material. This means complete failure of the accumulator. To close the accumulator the line tension must increase to move the block.
In the rotary type of accumulator schematically illustrated in FIGS. 4A and 4B, the inertia of the accumulator is its greatest disadvantage. During any speed change of the filamentary material, the material either becomes slack or high line tensions are applied.
The round accumulator that spreads open, which is schematically shown in FIGS. 5A and 5B, has a large mass so that it also has the same difficulties with controlling line tension as do the other accumulator types mentioned, supra.